ARTHRITIS OF THE KNEE JOINT

There are many designs of knee implants available to the surgeon. There is no universal agreement as to which design is best. Each surgeon selects what he believes is best, or what he was trained to use.

Metal parts of the implant are manufactured of Cobalt-chrome or Titanium. There is no agreement as to which is the better metal. But there is universal agreement that it is better if the metal part that moves on the plastic is made of cobalt chrome. The most important problem in the complex field of implant design is the issue of metal and plastic wear (resulting from parts moving on each other) and the tiny particles produced by such wear. These particles may cause adverse responses in the surrounding tissues and bone, resulting in loosening of the implant. The greatest amount of particles is produced by a titanium metal part moving against a plastic part. It is an area of continuing research.

The plastic parts of the implant are made of high-density polyethylene which has proved very acceptable over the years. Efforts are underway to develop “improved” polyethylenes.

The knee implant usually used by Dr. Huddleston is the “Low-Contact-Stress-Knee” manufactured by the Johnson and Johnson Corporation of Warsaw, Indiana. Its metal parts are of cobalt chrome. It has a rotating plastic bearing which improves the range of motion and greatly decreases wear of the plastic and the production of harmful particulates. A potential complication with the bearing is that it may “spin-out”, sometimes requiring re-operation (the operation is minor and the chances of this happening are less than 1/4%).

A frequently asked question is the weight of the implant: the knee implant weights between 15 and 20 ounces, depending on the size selected for you.